Nearly everyone can agree: The scene at the southern border is a horror.

Even those who somehow think that it isn't a moral horror to see little kids pulled from their parents and put in cages -- or, to use the preferred term among White House defenders, "chain-link partitioned holding areas" -- recognize that it is a political horror. If the politics weren't so bad, supporters wouldn't be so desperate to come up with more palatable euphemisms.

As ugly as things are, it's worth remembering that the Obama administration had similar struggles and similar responses. The point here isn't "whataboutism." It's simply to note that the U.S., not any particular administration, faces a very difficult challenge, shared by other economically advanced nations: Untold millions of poor people want to be richer, and they believe they can make that happen simply by moving here or to Western Europe. And they're right.

It may be 2018 on everyone's calendar, but that doesn't mean we all live in the same moment. Very poor people become richer by moving here because, in a sense, they are moving to the future.

Imagine you live in a poor village in Asia or Africa (or in Appalachia 150 years ago) where you still need to fetch water from a well or even a river a mile away. In terms of time used and energy exerted, you'd be richer if you moved to the U.S. even if you spent the rest of your life poor by our standards. Mere access to clean tap water, electricity and indoor plumbing is considered a luxury in some parts of the world. Not to mention the rule of law, human rights, freedom of conscience, etc.

By crossing the U.S. border, low-skilled Mexican laborers automatically become 10 to 20 times more productive. It's not because their work ethic magically improves. It's because our economy has countless productivity multipliers built into it, from better machinery to better laws and more efficient institutions and practices.

William Lewis, the former director of the McKinsey Global Institute, found that illiterate, non-English-speaking Mexican agricultural laborers in the U.S. were four times more productive than the same sort of laborers in Brazil. Take a Yemeni bus driver and put him behind the wheel of a bus in the U.S. According to economists Michael Clemens, Claudio Montenegro and Lant Pritchett, the Yemeni bus driver will become 15 times more productive doing the same job, mostly because the people he's driving around are more productive too.

This is not an argument for open borders. I simply want to point out that so long as there are very poor countries, very poor people will understandably want to move here. This would be true even if those poor countries had solved all of the other problems -- violence, anarchy, persecution -- that cause decent people to want to flee home.

In other words, supply will exceed demand for a very long time to come. Even if we tripled our intake of legal immigrants, more would still want to come.

The best long-term solution to this problem is to make poor countries rich as quickly as possible. In the meantime, the immediate challenge presented by this level of desire to immigrate to the U.S. is going to be less economic and more political and cultural. Immigrants bring new customs, values and ideas of how society should work. As the Swiss writer Max Frisch famously said of the guest workers his country imported, "We wanted workers, but we got people instead."

Waves of immigrants invite reactions. Many people like to call these backlashes racist, and in some cases they are. But they are also entirely natural, human responses to sudden cultural changes. German Chancellor Angela Merkel's government may fall because of one such reaction. (The 86 percent of Germans who want to see a more forceful approach to repatriation can't all be bigots.) Votes in favor of Brexit didn't strongly correlate with unemployment very much, but they did with attitudes on immigration.

President Trump's election was in part a reaction to high levels of immigration, legal and illegal. If people don't want unreasonable politicians to exploit immigration-fueled anxiety, then reasonable politicians on both sides need to take immigration far more seriously than they have so far. If they don't, things will get much worse than the spectacle on the border today.